This invention relates to pressure powered pumps.
Pressure powered pumps are known in which the flow of a liquid into and out of a pumping chamber is controlled by check valves, and in which the pumping action is achieved by the controlled admission of a gas under pressure, such as steam or compressed air, into the pumping chamber. The admission of the compressed gas, and its subsequent venting, is controlled by a float within the pumping chamber which acts on inlet and exhaust valves through a spring-loaded overcenter mechanism. The overcenter mechanism includes valve actuating means which operates the valves. As is common in valve operating linkages, there is a clearance in the linkage when the valves are closed so that the valves can engage the valve seats properly without obstruction from other parts of the linkage.
In the past, such clearances have been kept to a minimum in pressure powered pumps, so as to avoid lost motion in the valve operating linkages.
In a pressure operating pump, the inlet valve, when closed, is held in the closed position by the pressure difference between the compressed gas (such as steam) and the interior of the pumping chamber. Consequently, substantial force is required to open the inlet valve, this force being provided by the spring of the overcenter mechanism.
The pumping rate of a pressure powered pump is significantly affected by the sizes of the inlet and exhaust valves. To achieve a high pumping rate, large valves are required, but their sizes are limited by the force which can be applied to them by the operating mechanism comprising the float and the overcenter mechanism.